The operations of soldering and brazing are suggestive to some as being comparatively simple of execution, requiring no special degree of skill or experience on the part of the workman. As a matter of fact they involve a wide range of manipulation and frequently demand experienced workmanship of a high order.

At the same time so many mechanics are accustomed to perform soldering operations with poorly prepared tools and with appliances which might be greatly improved upon, that the author is led to offer this book in the hope that it will serve as a practical aid to improved methods, thereby serving the interests of mechanics who seek advancement as well as employers who are alert to the importance of efficiency and economy in the methods pursued in their establishments.

Therefore the author has dwelt with considerable fullness upon the many phases of soldering and brazing, giving the results of experience and observation acquired through long practice and experiment in these channels.

If the result is accomplished, of assisting operators to a larger appreciation of the requirements of expert workmanship in these really important branches of mechanics, he shall consider that the time and labor spent in preparing the treatise has been well applied.

Soldering is a very peculiar, although very common operation, whereby two metals, either similar or dissimilar, are united by a third metal by means of heat. Soldering, to quote from an ancient dictionary by Webster, is to unite with metallic cement. A more modem issue of Webster's dictionary says it is to unite metal surfaces or edges with solder. The old dictionary says that solder is a metallic cement.


Definition of Soldering

In reality, soldering is the joining of similar or dissimilar metals by means of an alloy which has a lower melting point, though this is not always the case. (According to modem practice), soldering means the uniting of two or more pieces of metal with an alloy of lead and tin. The usually accepted theory of soft soldering is that the molten soft metals, when under certain well known conditions adhere to and unite with the metals being soldered, at a temperature less than the melting point of the metals in question, but greater than the melting point of the solder or uniting alloy.


Burning or Autogenous Soldering.

There is a method of soldering which is used extensively when tanks are lined with sheet lead, which is known to the trade as "lead burning," but this operation should not be confused with soldering. Lead burning is really a form of welding and a newly developed system of autogenous welding, which is coming into quite general use. It is nothing more nor less than a “burning operation,” almost exactly like lead burning.

It is possible to unite tin and similar metals with low melting points, by melting their edges or surfaces together, but this is not truly soldering. In lead burning, the two surfaces are united by means of a strip of similar metal, which is used as solder and is melted into and with the metals to be joined. Thus in lead burning, the surfaces of the metals to be joined are actually melted, while in true soldering, the surfaces are not melted but are heated to a degree much less than their melting points and only a little hotter than the melting point of the alloy, which is used as solder.


Solders Commonly Used

The alloys most commonly used in soft solder have a wide range in their melting points. Some of the solders, notably those made chiefly of tin and lead, melt at a temperature as high as 500 to 600 degrees, while ordinary soft solder melts at 300 to 500 degrees. Solders may readily be made which will melt at any temperature down to 120 degrees or much less than the temperature of boiling water. Such solders are of little use commercially, being used mostly for exhibition purposes, for tricks and amusement. There is a notable exception in the automatic sprinkler head, which is dosed by a drop of solder, which melts at a very low temperature and which, when melted, permits water to escape from the sprinkler and extinguish the fire which caused the rise in temperature to the degree which melted the solder.


Fusible Plugs for Steam Boilers

Another use for low temperature solder or alloy is for filling fusible plugs, one of which is required by law in certain States to be placed in each steam boiler or generator. It is found, however, that although such a plug may be made to melt at any required temperature, that it will not melt at that degree of heat after it has remained in use for a considerable time. Being continually subjected to heat and pressure seems to change the character of the alloy so that the melting point continually grows higher; after plugs have been in use for a year or two they will not melt at the temperature of steam.

To obviate this difficulty, steam boiler specifications call for plugs filled with blue Banca tin, a metal, the melting point of which is not affected by continued heat. Still another application of low temperature alloys or solders is the uniting or mending of utensils made from block tin or of Britannia ware. Some very soft solders are made from the alloy of bismuth, still others contain mercury and by the use of this metal, solders may be made which will melt at any required temperature above 40 degrees Fahrenheit and below zero. It will thus be seen that the temperature range of solders is unlimited.

A very pretty operation is the making of a low temperature solder which will melt by the warmth of the hand and which will harden again at the ordinary air temperature of 70 degrees. Such solders are of very little commercial use save for making models and illustrating methods of doing work in the shop or in the school.

The following table gives the composition and melting points of various alloys, which may be of use in soldering. From this table the workman may take out a formula for making a solder, which will fill any condition likely to arise in the most extensive practice.


Silver Soldering

Silver soldering is really a form of brazing. Silver solder is usually known as hard solder, and is thus distinguished from soldering with the copper and alloy of lead and tin. Silver soldering is usually performed with the blow pipe, the articles to be soldered being wired together or otherwise held securely in place during the fluxing and heating operation! The best work in silver or hard soldering is secured when the parts are fitted together as closely as possible; the better the fit, the better will be the soldering.

A joint may be made perfectly by drilling a hole through both pieces of metal and joining them by means of a rivet, which may even be countersunk, and riveted at each end.. If such a joint be subjected to hard soldering or brazing, the silver or brass will, if the soldering be properly done, find its way along the rivet, through the drilled hole, and show itself at the opposite end of the rivet, no matter how tightly it may fit. The operation of silver soldering will be described in detail in another chapter.


Fluxes and Fluxing.

A great variety of fluxes may be used in soft soldering, in hard soldering and in brazing. Fluxes are used in soldering to prevent oxidization of the heated surfaces, both of metals to be united and of the uniting alloys, also to render the solder more fluid and thereby to penetrate better into the interstices between the parts to be soldered. Taking this view of the matter, it will be seen that almost any substance will serve as a flux which will melt and coat itself over the heated surfaces without being disturbed by the heat.

Conmion resin is the flux universally adopted for tin and brass - in fact, for soft soldering in general, for the reason that it will withstand a temperature which enables it to melt and spread over the surface of lead and tin without being driven off in a gaseous condition. For soldering lead, particularly when joints are to be wiped, the plumber uses tallow, which seems to be the best flux for this metal Resin may be and is used when soldering lead with the copper, but tallow works well and is handy when resin is not obtainable. In fact, cylinder oil, or any heavy grease, may be used, which will protect the surface of the metal from attack by oxygen of the air.


Lead and Tin Oxidization.

When metals are heated they are very readily attacked by oxygen. The dross which gathers in the molten metal in the ladle is an example. The dross is nothing more or less than oxide of lead caused by the union of metallic lead from the ladle with oxygen from the air. When lead or tin are in the solid form they are less readily attacked by the atmosphere. A very thin film of oxide forms almost instantly over a freshly cut surface of lead or tin, but this thin layer seems to protect the metal against further oxidization at ordinary temperature. It is for this reason that tin and lead seem to be free from rust, while they are actually covered with a very thin layer of rust or oxide, which effectually prevents further action of the elements.

A proof of oxidization is found in the odor which constantly arises from a piece of new tin. By pouring some water on a sheet of tin or into a new tin dipper, and holding it to the nostrils, one will readily detect the peculiar odor of tin, which shows that a coating of oxide has been formed over its surface by the union between metallic tin and oxygen.


Borax a Universal Flux for Hard Soldering

Borax may be used as a flux and for brazing and hard soldering. Borax or boracic acid are the agents universally employed for that purpose. Resin will not stand for brazing, because of the high temperature necessary, which drives all the resin into gaseous form and it becomes dispersed or lost before the brazing operation can be per- formed. Borax will melt over the surface and form a coating of glass, so to speak, which remains until the brazing operation has been completed.